Potentiometer apparatus



June 28, 1960 v. c. KENNEDY, JR 2,943,287 POTENTIOMETER APPARATUS Filed Oct. 6, 195

INVENTO ATTORNEYS.

United States Patent POTENTIOMETER APPARATUS Verne C. Kennedy, Jr., Norman, kla., assignor to Streeter-Amet Company, Grayslake, 111., a corporation of Illinois Filed Oct. 6, 1958, Ser. No. 765,551

' 8 Claims. (Cl. 338-91) This invention relates generally to potentiometer apparatus and more particularly to new and improved potentiometer apparatus of the type in which a given displacement of' the Wiper contact relative to the resistance element produces a desired change in resistance.

Precision type potentiometers generally are formed of a resistance element having a plurality of turns or windings of resistance wire, and a slidable wiper having an electrical contact in physical contact with a narrow band of exposed windings. Generally this narrow band of exposed windings extends normal to the direction of the windings so that movement of electrical contact along the band places it in contact with different portions of the resistance element. Those skilled in the art will readily appreciate that if the change in resistance is to be linear with displacement of the electrical contact, each of the turns must be separated by an identical distance and the total resistance around each turn also must be identical. Neither of these requirements can be readily accomplished except by the use of expensive precision equipment. To accomplish the first requirement it is necessary to wind the turns of resistance wire onto the insulating base with great accuracy and to secure them in place before any change in their position can occur. The second requirement is hampered by the fact that resistance wire generally has a non-uniform incremental resistance along its length, largely due to manufacturing difficulties.

As a result of these considerations, a linear potentiometer is very expensive and further it ordinarily has a relatively short operating life. In sharp contrast thereto, a potentiometer in which a high degree of precision is not required may be made considerably cheaper and with a substantially longer operating life.

Accordingly, it is a general object of this invention-to provide precision potentiometer apparatus which combines the dual desideratum of relatively low cost and of relatively long life.

It is a further object of this invention to provide potentiometer apparatus which utilizes relatively non-linear potentiometers and which automatically corrects for the non-linearities therein.

It is a still further object of this inventionto provide new and improved potentiometer apparatus, as described above, in which the variation of the wiper along its range of movement on the resistance element may be made to vary the resistance between the wiper and the fixed terminal of the resistance element in accordance with a desired predetermined law.

It is another object of this invention to provide new and improved potentiometer apparatus in which the rela- 2,943,287 Patented June 28, 1960 tionship between the displacement of the wiper contact and resistance element may be selectively adjusted in a desired manner.

It is still another object of this invention to provide new and improved potentiometer apparatus, as described above, which corrects for undesirable variations in the wiper contact displacement-resistance relationship after the potentiometer has been formed and assembled.

It is still another object of this invention to provide such new and improved potentiometer apparatus which is characterized by its flexibility and its relative economy of construction and operation.

These and other objects are realized in accordance with the features of one illustrative embodiment of the invention wherein the potentiometer, which advantageously may be a balance potentiometer in a bridge circuit, is provided with an extended shaft and the potentiometer body is cantilevered on the shaft bearings. In this manner, the potentiometer body itself is free to rotate as well as the potentiometer wiper. A roller member is positioned on the back face of the potentiometer housing and is adapted to ride on the surface of a flexible steel strip. In accordance with one aspect of this invention the roller is held against the surface of the flexible steel strip by means of a return spring secured to the potentiometer housing.

It is a feature of this invention that the flexible steel strip is provided with a plurality of adjusting screws disposed throughout its length so that selected portions of the strip may be adjusted in a plane transverse to the longitudinal dimension of the strip. The strip is mounted on a rack assembly which cooperates with a pinion coupled to the potentiometer shaft so that the flexible steel strip is moved back and forth in response to the rotation of the potentiometer shaft. In this manner the spring always returns to the same point at the potentiometer roller for a given position of the potentiometer wiper contact.

In accordance with an aspect of the invention, the movement of the flexible strip moves the potentiometer roller up and down and thus actually rotates the body of the potentiometer. As explained in greater detail below, it is this rotation of the potentiometer body for a given rotation of the potentiometer Wiper contact that compensates for potentiometer non-linearities. Accordingly,

an ordinarily non-linear potentiometer with long life characteristics can be used in precision work since the non-linearities may be compensated for by the rotation of the potentiometer body, as described above.

In accordance with the features of an alternative embodiment of this invention, the flexible steel strip may be used to operate a linear potentiometer in lieu of rotating the body of a balance potentiometer. Thus, the back and forth movement of the flexible steel strip in response to the rotation of the balance potentiometer shaft varies the resistance of the linear potentiometer. Since the linear potentiometer can be placed in the balance potentiometer circuit in such a manner that it electrically compensates for non-linearities in the balance potentiometer, this embodiment of the invention also permits the use of a relatively non-linear and long life potentiometer in precision applications.

The above and other features of novelty which char acterize this invention are pointed out with particularity in the claims annexed to and forming a. part of this specification. For a better understanding of this invention, however, its advantages and specific objects attained with its use, reference is had to the accompanying drawing and descriptive matter in which are shown and described several illustrative embodiments of the invention.

In the drawings:

Figure 1 is a perspective view of one illustrative embodiment of the invention;

Figure 2 is a side elevation, in cross section, of the adjustable steel strip and rack assembly; and

Figure 3 is ajperspective view of an alternative embodiment of the invention.

Turning now, to the drawing, and more particularly to Figure 1 thereof, there isshown an illustrative embodiment of the invention comprising a potentiometer 10, which advantageously may be utilized as a balance potentiometer in "a bridgecircuit. Potentiometer is formed of a :housing 12 having a resistance element secured to the inner surface thereof and a wiper shaft 14 having a wiper contact in electrical contact with the resistance element, in a manner well known in the art. Terminals 16 are provided on the housing 12 and these terminals are adapted to be connnected to the ends of the resistance element and to the wiper contact.

The potentiometer wiper shaft 14 advantageously is rotatably supported by the spaced support plates 19 and 21 secured to the base plate 18. A wiper shaft gear 18 is positioned between spaced plates 19 and 21 and serves to rotate wipershaft 14 when it, in turn, is rotated by drive gear 20. I

Drive gear 20 also rotates pinion shaft gear 22 and therefore pinion shaft 26, which is rotatably journaled in support plate. 25 so as to rotate the pinion 24, connested-at the-other end of pinion shaft 26. Those skilled in the art will readily appreciate that any suitable drive source, such as the balance motor of a bridge circuit, maybe utilized to rotate thepotentiometer wiper shaft 14 and pinion 24 during the operation of the invention.

In accordance with a feature of this invention, the body 12 of the balance potentiometer 10 is cantilevered on the bearings of the wiper shaft 14 so that it is free to rotate about shaft 14 as indicated by the arrow 27. Advantageously, a return spring 28 is secured between the base plate 30 and a link member 32 connnected to the balance potentiometer housing 12. A roller 34 on suitable bearings is rotatably secured to the end face of the potentiometer housing 12 and it can be seen that the exertion of force on the roller 34 causes the potentiometer housing to be rotated about the wiper shaft 14. The force for causing the potentiometer housing 12 to rotate in the counter-clockwise direction, as shown in Figure 1, is supplied by the return spring 28;, while the force. of roller 34 for causing the potentiometer body to rotate in the clockwise direction, as shown in Figure 1, is supplied by a flexible steel strip 36, in a manner now to be described.

Flexible steel strip 36 is positioned on rack assembly 38 having a rack 49 extending along the upper face thereof. As shown in greater detail in Figure 2, flexible steel strip 36 is sandwiched between the base of rack assembly 38 and a screw plate 42 extending the length of the steel strip and the rack assembly. In accordance with a feature of this invention, a screw plate 42 has disposed along its length a plurality of adjusting screws 44 which are positioned through the screw plate into contact with the steel strip such that adjustment of the screws 44 causes a corresponding positional variation in the flexible strip.

Thus, as shown in Figure 1, raising a screw 44 out of the screw plate 42 causes the portion of the flexible steel strip in contact therewith also to be raised. In this manner the flexible steel strip may be adjusted up and down along its length in any desired fashion to provide an adjustable cam surface for the roller 34.

The rack assembly 38 is positioned in a pair of rack guides 46 and 48 attached to base plate 30,*so that when the pinion 24 is rotated by the gear 22, the rack 40 is moved back and forth in the direction indicated by the arrow 50. The roller 34 on the potentiometer housing 12 rests upon the flexible steel strip 36 and as the rack is moved back and forth the roller, and therefore the potentiometer body 12, are rotated in accordance with the positional variations in the flexible steel strip.

Those skilled in the art'will appreciate that as the potentiometer wiper shaft 14 is rotated, potentiometer body 12 also is rotated in accordance with a preselected scheme which is determined-by adjusting the adjustable screws 44 in any desired pattern. In accordance with an important aspect of this invention, the rotation of the potentiometer body 12 may be preset to compensate for any non-linearities in the potentiometer resistance element to the end that thebalance potentiometer 10 may be of the relatively inexpensive-long life type. The adjusting screws 44 are adjusted for each potentiometer after the entire apparatus is assembled. The end result is a potentiometer apparatus with a long life and with a high degree of linearity.

An alternative embodiment of the invention is shown inFigure 3 of the drawing wherein similar elements have been given similar reference numerals. Thus, the balance potentiometer 10 is coupled by its wiper shaft to the potentiometer shaft gear 18 which in turn is meshed with the drive gear 20. Drive gear 20 also drives the pinion shaft gear 22 so that the pinion 24 drives the rack 40 back and forth as indicated by the arrow 50. The flexible steel strip 36 may be adjusted as described hereinabove by the various adjusting screws 44 disposed along the length of the rack assembly 38 and the screw plate 42.

In accordance with this embodiment of the invention the flexible steel strip 36 drives a-potentiometer 60, which advantageously is a linear potentiometer of the type wherein the shaft 62 slides in and out of the body 63 of the potentiometer. A return spring 64 is provided between the support plates 66 and 68 for operating the shaft 62 downwardly except when a raised portion of the steel strip 36 comes into engagement with the shaft 62 of the linear potentiometer 60.

Those skilled in the art will appreciate that the variation in the resistance of linear potentiometer 60 are in accordance with the corrections provided by the variations in the flexible steel strip 36, and therefore, the linear potentiometer 60 may be placed in the balance potentiometer circuit such that it electrically compensates for the non-linearities in the balance potentiometer 10. As explained heretofore this compensation may be set as desired by suitable adjustment of the adjusting screws 44.

I have shown and described two illustrative embodiments of my invention wherein the non-linearities of a potentiometer may be compensated in an inexpensive and readily adjustable manner. In accordance with the device of Figure 1, the potentiometer non-linearities are compensated by physically rotating the body of the potentiometer in a predetermined manner related to the shaft rotation, while in the device of Figure 3 the balance potentiometer non-linearities are compensated by utilizing a second linear potentiometer which has its resistance varied in accordance with the balance potentiometer non-linearities.

Those skilled in the art will readily appreciate that the principles of the invention may be used to vary the resistance of a potentiometer in accordance with any desired law. Thus any desired resistance characteristic may be obtained for a given potentiometer by varying its normal resistance in the manner described above by means of an adjustable flexible strip. Thus while there has been shown and described two specific illustrative embodiments of the invention it will be obvious to those skilled in the art that various changes and modifications may be made therein without departing from the principles of the invention, and therefore, it is intended to cover in the appended claims all changes and modifications as fall within the true spirit and scope of the invention.

What is claimed as the invention is:

l. The improvement of potentiometer apparatus comprising a potentiometer including a housing, a resistance element supported by said housing and a rotatable shaft having a wiper contact at one end thereof in sliding engagement with said resistance element, driving means coupled to said rotatable shaft for selectively positioning said wiper contact on said resistance element, an elongated strip of flexible material, a rack assembly supporting said strip of flexible material, means for selectively adjusting portions of the strip transverse to the rack assembly to form a cam surface, pinion means coupled to said driving means and engageable with the rack assembly for moving the cam surface of the flexible strip back and forth in accordance with the wiper shaft rotation, and correction means engageable with said cam surface providing a correction movement for each operative position of the potentiometer wiper contact relative to the potentiometer resistance element whereby movement of the cam surface of said elongated strip in accordance with the wiper shaft rotation causes a corresponding relative movement between said resistance element and said wiper contact to correct for non-linearities in said potentiometer.

2. The improvement of potentiometer apparatus comprising a potentiometer housing having a rotatable wiper shaft extending therefrom, driving means coupled to said rotatable wiper shaft for selectively positioning said wiper shaft relative to said housing, an elongated strip of flexible material, a rack assembly supporting said strip of flexible material, means for selectively adjusting portions of the strip transverse to the rack assembly to form a cam surface, pinion means coupled to said driving means and engageable with the rack assembly for moving the cam surface of the flexible strip back and forth in accordance with the wiper shaft rotation, and correction means engageable with said cam surface and movable in response to the back and forth motion of said flexible strip for providing a predetermined correction for each operative position of the potentiometer wiper shaft by causing a corrective movement of said wiper shaft relative to the potentiometer housing in accordance with the transverse amplitudes of the flexible strip cam surface.

3. The improvement of potentiometer apparatus comprising a potentiometer including a housing, a resistance element supported by said housing, and a rotatable shaft having a wiper contact at one end thereof in sliding en gagement with said resistance element, driving means coupled to said rotatable shaft for selectively positioning said wiper contact on said resistance element, an elongated strip of flexible material, a rack assembly supporting said strip of flexible material and including a plurality of adjusting screws disposed along the length of the strip for enabling portions of the strip to be adjusted transverse to the rack assembly to form an adjustable cam surface, pinion means coupled to said driving means and engageable with the rack assembly for causing the flexible strip to be moved back and forth relative to the potentiometer housing, and roller means rotatably mounted on said potentiometer housing in operative engagement with the flexible strip whereby corresponding movement of said potentiometer Wiper shaft and said rack assembly rotates the potentiometer housing relative to the wiper shaft in a selected manner as determined by the adjustable cam surface of the flexible strip.

4. The improvement of potentiometer apparatus comprising a potentiometer housing having a rotatable wiper shaft extending therefrom, driving means coupled to said wiper shaft for selectively positioning said wiper shaft relative to said housing, an elongated strip of flexible material, a rack assembly supporting said strip of flexible material and including a plurality of adjusting screws' disposed along the length of the strip for enabling portions of the strip to be adjusted transverse to the rack 5. The improvement of potentiometer apparatus comprising a potentiometer housing having a rotatable wiper shaft extending therefrom, said housing being cantilever supported by said wiper shaft so as to be freely rotatable thereon, an elongated strip of flexible material, a rack assembly supporting said strip of flexible material and including means for enabling portions of the strip to be adjusted transverse to the rack assembly to form an adjustable cam surface, driving means coupled to said wiper shaft and said rack assembly for causing the flexible strip to be moved back and forth in accordance with the rotation of said wiper shaft, roller means rotatably mounted on said potentiometer housing in operative engagement with the flexible strip whereby corresponding movement of said potentiometer wiper shaft and said rack assembly causes the potentiometer housing to be rotated relative to the wiper shaft in a selected manner determined by the adjustable cam surface of the flexible strip.

6. The improvement of potentiometer apparatus in accordance with claim 5 further comprising return spring means connected to said potentiometer housing for urging the housing to rotate in a direction opposite to the direction of rotation caused by said cam surface.

7. The improvement of potentiometer apparatus comprising a first potentiometer housing having a first resistance element and a first wiper contact with a rotatable shaft extending therefrom, driving means coupled to said rotatable shaft for selectively positioning said first wiper contact on said first resistance element, an elongated strip of flexible material, a rack assembly supporting said strip of flexible material, means for selectively adjusting portions of the strip transverse to the rack assembly to form a cam surface, pinion means coupled to said driving means and engageable with the rack assembly for moving the cam surface of the flexible strip back and forth in accordance with the wiper shaft rotation, and correction means including a linear potentiometer having a second resistance element and a second wiper contact with a sliding shaft engageable with said cam surface for providing a correction movement in response for each operative position of the first potentiometer wiper shaft relative to its housing whereby movement of said cam surface of the flexible strip in accordance with the rotation of said first potentiometer wiper shaft causes a corresponding relative movement between said second resistance element and said second wiper contact to provide said correction movement.

8. The improvement of potentiometer apparatus comprising a first potentiometer including a housing, a first resistance element and a first wiper shaft, an elongated strip of flexible material, a rack assembly supporting said strip of flexible material and including a plurality of adjusting screws disposed along the length of the strip for enabling portions of the strip to be adjusted transverse to the rack assembly to form an adjustable cam surface, means coupling said first wiper shaft to said rack assembly for causing the flexible strip to be moved back and forth in accordance with the shaft rotation on said first resistance element, and a second potentiometer having a second: resistance element'and a second Wiper shaftin operative--engagement-with the flexible strip; whereby corresponding movement of saidfirst potentiometer wiper shaft and -said-rack assembly actuates the second wiper shaft-of-said' second potentiometer in a selected manner determined by-the adjustable cam surface of the flexible strip to cause relative-movement between "said second resistance elementand said second wiper shaftto provide a correction for non-linearities in saidfirst' potentiometer.

References Cited in the file of this patent UNITED STATES PATENTS in. on 

